Help identifying this Date Just

[Cinquecento]

Hello,

I'm hoping the experts here can help verify the authenticity and help me better understand what this watch is exactly.

Back story, it' was purchased in the mid 80's by a family member who doesn't know much about watches. no box no papers. Not sure what the serial is. What throws me off is the Rolex engraving on the back and the face looks a bit off to me. But I am no expert.

Thank you.